1. Field of the Invention
The present invention relates to a surface-emitting semiconductor laser capable of emitting a laser beam from the surface thereof, and particularly, to a surface-emitting semiconductor laser appropriately applicable to a case where single-mode optical output is necessary.
2. Description of the Related Art
In the surface-emitting semiconductor laser emitting light in a direction perpendicular to a substrate, a plurality of elements can be arrayed on the same substrate in a two-dimensional shape. For example, when a surface-emitting semiconductor laser arrayed in a two-dimensional shape is used as a light source for digital copy apparatuses or printers, pixel information can be input onto a photoconductive drum in a parallel process, thereby achieving high density and high speed. Accordingly, the surface-emitting semiconductor laser has recently been used as the light source of digital copy apparatuses or printers.
The surface-emitting semiconductor laser used as the light source of printers has been commercialized by several makers. However, the wavelength band is restricted to an infrared band (770 nm to 790 nm). When the oscillation wavelength can be made to be shorter, a beam spot can be made smaller. Therefore, a high precision printer can be realized. Accordingly, a surface-emitting semiconductor laser of a red band which can be used as the light source of printers has recently been developed.
For example, U.S. Pat. No. 7,359,421 discloses a technique capable of oscillating the surface-emitting semiconductor laser of a red band as a single lateral mode. In U.S. Pat. No. 7,359,421, since current narrowing of an oxidized layer achieves a strong refractive index distribution, it is asserted that the property of the single mode is not excellent. In U.S. Pat. No. 7,359,421, a gain guide structure by ion implantation is used to realize a weak refractive index distribution. Moreover, since the current narrowing layer is formed by two-time ion implantation, a variation in the refractive index is inhibited due to a thermal lensing effect. In U.S. Pat. No. 7,359,421, it is asserted that single mode oscillation of high output can be achieved since the lateral mode can be controlled by the broad current narrowing. The inventors of U.S. Pat. No. 7,359,421 published a paper (SPIE Vol. 6484 Vertical-Cavity Surface-Emitting Lasers XI, paper 6484-04) about the surface-emitting semiconductor laser of a read band. In SPIE Vol. 6484 Vertical-Cavity Surface-Emitting Lasers XI, paper 6484-04, it is not clear that the configuration of U.S. Pat. No. 7,359,421 is used. However, when it is assumed that the configuration of U.S. Pat. No. 7,359,421 is used, the optical output of the signal mode is reliably achieved with 2.8 mW at the ambient temperature.